This application is related to the subject matter of commonly owned, co-pending application Ser. No. 10/677,524, filed on even date herewith, the specification of which is incorporated herein by reference.
The invention relates to a test apparatus for testing substrates at low temperatures, having a chuck, which can be displaced in the working area by means of a chuck drive and can be cooled using suitable cooling apparatus. The test apparatus includes a receiving surface for receiving a test substrate, comprising a substrate carrier and component to be tested, and a holding arrangement for receiving the substrate carrier.
The test substrate may comprise either semiconductor chips which are still joined to the wafer, or individual components, such as semiconductor chips, hybrid components, micromechanical components or the like. The substrate has a smooth and planar underside and is arranged and held, at least indirectly, on the chuck, which has a smooth and planar receiving surface. The test substrate can be displaced with the chuck in the working area by means of a chuck drive, so that it can be positioned in relation to the contact-making needles. Positioning in the horizontal plane is generally effected by an X-Y table, which also an orientation angle adjustment in the range of a few degrees.
The operational reliability of electronic components is preferably tested under the environmental conditions which correspond to the conditions of use of the component in question. In this context, testing at temperatures below the freezing point of water is a focal point.
To set these test conditions, the working area of the test apparatus is generally surrounded by an enclosure. A test apparatus having a housing of this type is known from DE 4109908 C2. In the case of this test apparatus, the enclosure has a plurality of inlet openings in the lower section and a further opening, which serves both as an outlet opening and to provide test probe access in the upper wall of the enclosure. When testing in the relatively low-temperature range, a gas flow is provided through the working area by means of these openings, in order to prevent the precipitation of moisture from the surrounding atmosphere on the test substrate. However, these test conditions restrict the possible low temperature range for the testing of electronic components.
In addition to receiving and positioning the test substrate, the chuck is also used to set the temperature at which the testing of the test substrate is to take place. For this purpose, a suitable coolant is applied to the chuck. To set the temperature or further controlled test conditions at the chuck, the latter is connected, via fluid lines, to the corresponding coolant source located outside the working area. On account of heat exchange with the chuck drive, which is in thermal contact with the chuck, the chuck drive is likewise cooled. In the test apparatus described, the cooled chuck drive constitutes a particular drawback, since the positioning of the chuck relative to the probes can only be effected with the reproducibility and accuracy required for the test substrate with considerable outlay on time and labor. The media connections and lines, which are relatively rigid at relatively low temperatures, further exacerbate this drawback.
A further drawback consists in the fact that the temperature of the test substrate is influenced by the surrounding components of the test apparatus, the temperature of which has been set very differently by the various heat exchange processes in the equilibrium state. For example, high levels of heat are introduced into the test substrate as a result of uncontrollable thermal radiation and convection from the surrounding hot components, which has a significant adverse effect on the accuracy and reproducibility of the testing.
For the testing to be carried out, the test substrate has test probes applied to it, in the form of contact-making needles with electrical input signals, and the output signals are measured using additional probes. The output signals may be of various types and may also be produced by other input variables, such as for example radiation in different wavelength regions. The probes are generally located outside the working area, on the upper housing closure, and make contact with the components through the above-described opening located in the top of the housing, either directly or indirectly via contact-making surfaces which are present on the test substrate. When the components are being tested at relatively low temperatures, the fact that the probes are at room temperature firstly means that the geometry of the probes does not coincide with the geometry of the test substrates in the cooled state. Secondly, the contact between the test substrate and the warmer probes leads to a temperature drift at the substrate and therefore to a change in the test conditions. These facts also have a significant adverse effect on the accuracy and reproducibility of the testing at relatively low temperatures.
Accordingly, the invention is based on the object of providing a test apparatus for testing substrates at low temperatures in which spatially and thermally defined test conditions can be set and maintained with minimal outlay on energy and labor both at room temperatures and at low temperatures.